6.5 Optimizer to 6.2 Differences (bolts and anything else)

[adf5565]

Well after the issues I encountered with my 6.2 block and failed rebuild I decided to purchase a new 6.5 Optimizer. I'd like to have everything I need on hand when it arrives so ideally it is a fairly quick swap and I don't have to wait for parts.

I've heard that the few remaining bolts on the 6.2 that were standard thread are now metric on the Optimizer. However, I can't seem to find a list of which exact ones these are and the correct metric replacement for them. I believe two of them are:

- Bellhousing bolts
- Motor mount bracket to engine bolts

I'm looking for assistance on whether there are any other bolts of interest that also are not compatible from the 6.2 and what is the correct metric replacement for the ones I've mentioned as well as any others. Also I would like to know if there are any other differences between the Optimizer and 6.2 that are of note which will require different adapters/fittings/etc. The only other item I'm aware of is the oil cooler line block fittings are a larger NPT thread (I believe 1/2" vs 3/8") but I already have replacements on the way from Leroy Diesel there.

 

[Barrman]

Yes, the Optimizer is all metric. I thought every 6.2/6.5 was all metric. President Carter tried to get Congress to convert the US to metric. They debated and it dragged on. Even today it takes 2-3 years to go from idea to production in the auto industry. So, Detroit Diesel while designing the 6.2 thought it was going to be Federally mandated to be metric by the time it entered production started off making the engine all metric.

When I switched my M715 from a Big Block 396 to a 6.2 I sure thought I had to go with metric bell housing bolts. But that was 10 years ago. I could be wrong. I know the motor mount to block bolts are metric on a 6.2. I have done that in the past year With engines in a can.

 

[adf5565]

Yes, the Optimizer is all metric. I thought every 6.2/6.5 was all metric. President Carter tried to get Congress to convert the US to metric. They debated and it dragged on. Even today it takes 2-3 years to go from idea to production in the auto industry. So, Detroit Diesel while designing the 6.2 thought it was going to be Federally mandated to be metric by the time it entered production started off making the engine all metric.

When I switched my M715 from a Big Block 396 to a 6.2 I sure thought I had to go with metric bell housing bolts. But that was 10 years ago. I could be wrong. I know the motor mount to block bolts are metric on a 6.2. I have done that in the past year With engines in a can.

Maybe it is just the bellhousing bolts then. I recall that was a 3/8 bolt on my 6.2 as I changed some of them when I had the transmission out last year. But I’ll double check to confirm. That’s good to know the motor mounts are already metric so that’ll save some searching.

 

[87cr250r]

In addition to the bellhousing and motor mount bolts, the oil cooler lines are 1/2 NPT on the Optimizer. You'll need to bush down to 3/8 if you want to reuse your 6.2 fittings.

 

[87cr250r]

Other things to consider, the torsional damper from a 6.2 will not work on the optimizer.

The water pump backing plates varies depending on which water pump you end up running.

You need to get one with cylinder heads that match your intake configuration. Angled vs straight holes. You'll need straight holes to work with the 6.2 intake.

 

[adf5565]

Other things to consider, the torsional damper from a 6.2 will not work on the optimizer.

The water pump backing plates varies depending on which water pump you end up running.

You need to get one with cylinder heads that match your intake configuration. Angled vs straight holes. You'll need straight holes to work with the 6.2 intake.

Thanks for the heads up! I have a fluid damper I’ll be swapping over so I’ll be able to leave out the spacer and it should be good there. I ordered the side mount turbo version so I believe the 6.5 intake I have should bolt up.

I also got a “dummy” crank position sensor to plug that hole on the timing chain cover. I’ve been told the 6.2 water pump backing plate will match, I'm sticking with the v-belt setup so pump will stay the same.

 

[Finnegan1008]

Do all Optimizers work NA? Or is it a specific model?

 

[87cr250r]

The intake manifold bolt holes are different between the NA and turbo Optimizers. Because of that, no not all Optimizers work NA.

 

[Barrman]

The intake bolt angle at the head of either vertical for the turbo heads or 60° from vertical for the non turbo heads. You also have the turbo oil feed and oil return in the valley. Both can be plugged. A center mount turbo 3 piece intake can be used without the turbo. You just need to play around with some tubing and elbows to make a filter set up. Here is a video of how I made a center mount turbo intake work with a Banks Sidewinder turbo:

 

[87cr250r]

If you have any buddies with a machine shop, you can also Loctite some bolts in the holes, mill them flush and redrill straight.

 

[khamill2000]

The intake bolt angle at the head of either vertical for the turbo heads or 60° from vertical for the non turbo heads. You also have the turbo oil feed and oil return in the valley. Both can be plugged. A center mount turbo 3 piece intake can be used without the turbo. You just need to play around with some tubing and elbows to make a filter set up. Here is a video of how I made a center mount turbo intake work with a Banks Sidewinder turbo:

Great video, thank you. I am looking at doing something similar. Did you happen to make any more adapters from that length of pipe you bought? The engine I bought came with the center mount turbo and I was considering cutting off the part that feeds into the intake and working from there.
I had previously found this but it costs more than I paid for the engine.

Center Mount to Side Mount Conversion High Flow Plenum – Quadstar Tuning LLC

 

[Barrman]

No, I did not make any more. If you aren’t using a turbo. I would suggest PVC pipe necked down with a grinder that has a 135° silicone elbow like mine at the bottom. Then an open air filter element installed above the IP. Just make the PVC pipe long enough to be sitting on the bottom of the valley when the cross plenum is bolted down. No pressure means no flying off.

 

[adf5565]

Turns out both the transmission bell housing bolts and the motor mount bracket to block bolts were indeed standard thread on my 6.2 and now metric on the 6.5 Optimizer. The new correct thread size is M10-1.5 for both bolts.

The motor mount bolts previously were 1-1/8” long so I ordered 30mm long replacements, while the bell housing bolts were 1-3/8” so I went with 35mm long.

 

[adf5565]

One additional thing I’ve come across that’s different is the oil pan. They visual seem very similar but the oil dipstick location is higher on the 6.5 than on the 6.2. Only realized it because the dipstick tube wasn’t lining up with the bolt on the exhaust manifold for securing it.

I’m assuming the 6.5 pan still fits in the CUCV, correct? And I should just change to a 6.5 dipstick tube? I could probably still make the 6.2 dipstick tube work with some tlc too

 

[87cr250r]

Yes, the 6.5 pan will fit your CUCV frame. I made a new dipstick tube out of some copper tubing. I brazed a wire ring in the bottom as a stop, cut the tube a little long, bent it to fit, brazed a bracket to grab an exhaust bolt, put 7 quarts oil in the pan (-1 for the filter), cut the top of the tube until the stick read full.

I was wondering why I had to trim 1/2" more than expected and why the 6.2 tube didn't fit. I never realized they had changed the height of the fitting. The 6.5 has an extra bolt boss near the motor mounts that hits the 6.2 dipstick tube so that shut me down there.